function volforce = out_f(xx,lambda,mu)
x=xx(1,1);
y=xx(1,2);
volforce = zeros(size(x));

volforce(1,1) = -((lambda+2*mu)*(2*2/mu+(2/(x^2 + y^2 + 1) -...
               (4*x^2)/(x^2 + y^2 + 1)^2)/mu)+...
              (lambda+mu)/mu*(-(4*x*y)/(x^2 + y^2 + 1)^2)+...
               mu*(2*2/mu+(2/(x^2 + y^2 + 1) - ...
               (4*y^2)/(x^2 + y^2 + 1)^2)/mu));
volforce(1,2) = -((lambda+2*mu)*(2*2/mu+(2/(x^2 + y^2 + 1) -...
               (4*y^2)/(x^2 + y^2 + 1)^2)/mu)+...
              (lambda+mu)/mu*(-(4*x*y)/(x^2 + y^2 + 1)^2)+...
               mu*(2*2/mu+(2/(x^2 + y^2 + 1) - ...
               (4*x^2)/(x^2 + y^2 + 1)^2)/mu));       



